While mechanisms associated with mitotic regulation are conceptually an attractive target in attempts to reduce tumor cell growth, compounds with high specific activity and selectivity and desirable pharmacological profile have been elusive. For example, the spindle apparatus can be targeted with spindle toxins (e.g., taxanes, vinca alkaloids, etc.) with relatively high activity, but many spindle toxins are unacceptable for pharmaceutical intervention as such poisons are often non-specific.
To improve specificity of treatment, components for spindle and kinetochore regulation or mitotic checkpoint control may be selected that have been shown to be functionally associated with cancer. For example, Hec1 is a critical component in spindle checkpoint signaling that is highly expressed in cancer and helps assure correct segregation of chromosomes during cell division. Hec1 interacts with various other kinetochore components including Nuf2, Spc 24, Spc25, and Zwint-1, as well as with mitotic kinases Nek2 and Aurora B. Overexpression of Hec1 is a common feature of a large variety of cancers and cancer cell lines, and can often serve as a prognostic marker in primary breast cancer and other cancers. Based on the apparent importance of Hec1 in tumor cell growth, inhibitory MA (siMA) has been used to reduce Hec1 expression and has shown considerable promise, at least in an animal model. However, in vivo delivery of effective amounts of siMA with high specificity to the tumor is often problematic.
More recently, various small molecule inhibitors have been developed that interfere with the Nek2/Hec1 interaction. Since Nek2 is a regulatory component of Hec1 in mitosis, abrogation of the Hec1/Nek2 function was expected to result in chromosome mis-segregation and cell death. Several promising compounds have been reported (see Qiu et al, J. Med. Chem., 2009, 52 (6), pp 1757-1767; Wu et al, Cancer Res. 2008 Oct. 15; 68(20):8393-9) that had significant cell killing activity and directly targeted the Hec1/Nek2 pathway. These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. However, while the observed activity was in at least some cases promising, problems associated with solubility, toxicity, and the need to use relatively high concentrations in order to be effective nevertheless remained.
Thus, there remains a pressing need for improved compounds, compositions, and methods for Heel inhibition, particularly as it relates to use of such compounds in the treatment of cancer and other proliferative diseases.